This movies has a certain underlying Groundhog Day-ish feeling to it, but in this instance it's voluntarily made. It shows us a different kind of "self-made" time travel, with a main character being in a downward spiral into insanity who can only go back in time for 24 hours at a time of their choosing. That concept is actually pretty interesting but throughout only superficial, sadly. It misses some marks where it could have gotten a deeper meaning about love, time travel and stuff.
How (or why) the time travel is achieved is irrelevant, portrayed in the movie by using a tan bed and saying this is a time machine, in a nail salon, let's go.

At parts like those, it's silly, at others it's cute af, but always somewhat toxic.
Our main heroine, Sheila, is suicidal and decides one day to kill herself but gets a last few drinks in a bar.
There she meets her "true love" Gary, with whom she has the perfect date over and over again for a year until she gets weary of his personality and antics. In reality, she fixates on him, obsesses over him to make him the best version possible with the help of some time travel into his past, playing his uncle so he has a father figure in his live and such. After some time she starts to constantly tell him, she's suicidal, she's going to kill herself, this is the place she would do it and such. Driving him away each time but she never let's him go.
You could argue she distracts herself from her suicidal tendencies because she doesn't "really want to kill herself" but that is still a sign of her bad state of mental health. She never kills herself in this simply because the time travel isn't automatically done as in Groundhog Day, killing herself would mean she can't go back 24 hours to meet Gary again.

The issue with that, when we ignore time travel for a second, Sheila is emotionally abusive towards Gary. She uses her suicidal tendencies to guilt trip Gary into a relationship at the end and we, the audience, are supposed to think aww cute they get together after all due to love. But no, there's nothing healthy about this.

For Gary there's always this contrary feeling of loving her and wanting to throw her "in front of a train" as he said. But he can never leave without having to fear she's going to kill herself. The fact that he, at the end, let's her decide on her own does not negate this underlying issue and feeling he has in their relationship.
There's nothing cute about toxic, abusive relationships and movies should not romanticize them.
That's where this otherwise cute, "fluffy" movie takes a weird, dark turn and falls apart.

Cuoco/Davidson portray their characters good, though.
It's a so-so movie, with good and bad parts but an intriguing concept that is not fully explored.